Known optical elements are films on which a “moth-eye structure”, a kind of nanometer-sized projection and recess structure (nanostructure), is formed (e.g. Patent Literatures 1 to 5). The moth-eye structure may be one including many nanometer-sized cone-shaped projections on the front surface of a base material, for example. Such a moth-eye structure has a continuously changing refractive index from the air layer to the base material to cause the front surface of the base material to be non-optical for incident light, significantly reducing the reflected light.